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Interesting article, as usual. The standards on indoor air speed was particularly new to me.

Western Europe has more comfortable climate than most of the US; they're further north, and on the west coast of a continent. I live near Boston, which is pretty far north for the US, and even so we've recently had A/C-only weather, temperatures of 33 C and humidity 60%, dew point 25 C (26+ is when some people start dying, according to wikipedia, and 24-26 is "oppressive".) For a lot of the US, like the Southeast, I suspect good architecture and fans still just ameliorate the climate, as opposed to making it comfortable.

Architecture could be better, but often will have higher embedded energy costs, and of course it'd be expensive to simply replace what we have, flawed as it is.

Location could be better: the west coast and the southwest make cooling much easier (various mixes of moderate temperatures, ocean breezes, low humidity and cool nights) but then of course there's the water problem. We could probably use a lot less energy if the US (or world!) lived in dense cities in the coastal west or southwest, but we'd need to be pumping in a lot of water or recirculating what we used much better.



One thing I've wished for is a dual mode A/C or something. My window unit's fan mode just recirculates indoor air, and I think that's normal. Probably simplifies the design, but it makes hard to cool efficiently given erratic summers. Many days (or nights) a window fan would be fine, but I'm not going to wrestle the unit down and up, especially when that means redoing my makeshift plastic insulation on the sides. So I use the A/C all summer even though I'd like the option to not do so.

Expense: my default power bill is around $18 for electricity. Fridge, lights, computer, ceiling and window fans... I think the fridge dominates, really. But with just one 5000 BTU window unit, it's $36 for the past month, and last year it went as high as $60 one month. Definitely a big difference! Maybe better insulation would help (I tape up bundles of plastic shopping bags on the sides), but still. The drawback of high mass wall buildings is that when they do heat up, they've got lots of heat to give back to you...



Great article again, thanks.

I think there's a mistake under section 'Why AC is Inefficient'

'The larger the space and the fewer the people within it, the more energy it will take to cool the occupants.'

FEWER People should instead be MORE People right?

Kris De Decker


@ Dan

It should actually read "...the more energy it will take to cool EACH occupant."

Thanks, corrected



Interesting comment about not being able to cool the skin with air that is warmer than it. The skin is cooled partly due to the evaporation of sweat (which coincidentally is similar to how aircon cools air by evaporating a coolant). This could happen with warm air too, in a similar way to how gas fridges burn gas to evaporate a coolant and cool down. I think you're right though, as this happens on a small scale unless you apply more water to your skin. In central Europe, outdoor fans spray 'mist' to achieve this.



Another great article. I have acquired something of a distaste for AC for personal reasons. The 'old man' of the house(condo actually), is extremely OCD when it comes to AC. He runs it constantly and obsessed over single digit changes to the temp reported by the thermostat. For example, if the interior temp is 80F, and the AC is, or even if its 78, then the AC has to been turned on immediately to bring it down to the 'required' 75F. It doesn't just run during the day, but 24/7 all summer long. Now hes the type of individual you cant say anything to, but once in a while, I am able to point out that humans will not melt into puddles of shapeless wax about 75F-files right over his head. I dont buy into the old people need to keep cool trope, but North Americans simply cant live w/o there AC, even in temperate Northern Canada! I often wonder what they do when AC is no longer widely available, melt?, die of heat stroke at 85F? Who knows? One side effect of this, there are tons of AC house bunnies that make zero effort acclimatize themselves to warmer summer temperatures-instead, like my old man, prefer to retreat indoors and stay there within their AC cooled shacks.Occasionally, they will forray outside to engage in something called 'golf', which is always generates endless talk of how 'hot' it was-but also how they managed to brave the harsh conditions on the golf course for several hours. Naturally the end goal of all this, was to return to an AC'd box as quickly as possible. I bike everywhere and acclimating myself to hot temperatures is not that a big a deal. If I stayed indoors all summer, Not only would would get nowhere-but I would also become (physiologically) dependant on artificial cooling-which is what I see happening in my own household-its bizarre to watch really. I dont if anyone has seen this, but I find, some peoples reaction to NOT being AC'd akin to withdrawal symptoms. They become quite irritable, and quickly.

A couple of other features that KdK didn't specifically mention but also problem with AC, is the *noise*. Really, Our AC unit sits in a small enclosed room which is a TV room(I dont use it often), but when unit cycles, as it does constantly, its like a jet engine. Whether your watching the idiot box or even if you wanted to a read a book-you cant-not in that room. Nor can you enjoy the deck outside in the evening either. The exterior vents are so loud it reminds of the noise levels I am exposed to biking on the highway(No choice in that matter either).

Another issue that AC causes was a study I read that looked at how AC affects people physically. One conclusion was that AC makes, or helps, make you fat. The reason being, humans respond to cold temperatures by wanting to eat more-to store up food, whereas warm temperatures tend to have the opposite effect, and suppress the urge to eat endlessly. There is much truth in that observation. Our other condo has no AC and I remember clearly in the summer, our meals were small, light and everyone lost weight and on no one was constantly munching all the time. And everyone felt fine-if a little on warm side. In the current structure, with the AC going full tilt-its big meals constantly and I am always fighting down the (unnecessary) urge to snack and feed my face-as it were. Biking 20-40k a day is probably what's saving my gut from expanding to North American standards, while the AC, OtOH, is telling me 'eat more food'.

Another great article thank you-sorry if my comment is a little OT.

Richard Miller


It should be a requirement that A/C systems can only be installed in conjunction with Solar PV and that Solar PV is installed for all existing A/C systems above 1kW rating within a reasonable time. The problem with Solar in northern Europe is that it doesn't generate during the peak demand in the evening and winter but it is ideal anywhere with peak electricity demand for A/C.

Mario Stoltz


Hello Kris,
thanks for the great article, very useful food for thought, as always!
An interesting aspect about the AC debate is integrated heating/cooling technology. Of course, this is (nearly) only relevant for new construction.
In all the climates where you need to heat in winter, cooling in summer can help reduce the winter energy bill. Heating systems for new builds increasingly make use of heat pumps. Most run on air temperature exchange for their ventilation system, but more than just a few are using the ground as a heat buffer. Ground / often really groundwater a few meters below the immediate soil will have the average yearly temperature of your region of the world (in northern central Europe, about 8°C). This is easily "warm" enough to heat your home in winter with a heat pump system.
In the same way and with the same equipment (if it has been set up for that mode), you can cool the house in summer. If the ground volume under your house is enclosed (like a water lens, rather than a groundwater "stream"), these two modes of operation will actually enhance each other. Cooling in summer will pump heat energy into the ground, which you can harvest back in winter, and vice versa. The energy required to run the system is far outweighed by the savings in heating/cooling energy.

In my own house (24 apartments) we have a forced ventilation system with central heat pump unit for energy recovery in winter. The heat pump is turned off in summers, but it is amazing how even the moderate airflow of the ventilation system makes you more comfortable. Compared to all the houses / apartments that I have lived in previously (none of these having a ventilation system), warm summer days are much more bearable.

Andre L.


I read the UC Berkeley study. I think there are a few caveats there in terms of it applicability to office environments, in no particular order of importance:

1) sandals and light t-shirts are not typical outfitting most people dress up on most office-jobs in the Western developed world

2) the article mentions discomfort after third break, and adaptation period. How much worse further sedentary work periods wound become, as most office jobs last much longer than the 2 hours the experimented involved

3) longer periods of light sweating that is evaporated leave the body with a salty sticky coat, which is uncomfortable and dirt in some sense.

4) silly as this might appear to be, hot air + wind + light evaporated sweat is bad for makeup on women and for hairstyles that involve anything besides natural form.

5) 80% humidity is a bad environment for computers, other electronics and furniture to being with.

6) the air flow on the experiment chamber is much higher than what is usually found on office buildings. This is positive for the experiment (facilitate creation of each controlled atmosphere), but it also increases the comfort of those in the chamber compared to the sticky and smelly air that would be created in an office full of people with their own smell-production and chemicals mixing up on a high-humidity environment with much more stagnant air.



One drawback of fans not mentioned in the article is the noise they generate, even if it is low level. The noise makes it very difficult for me to fall asleep in a room with a fan, and I'm probably not alone. Granted, AC units generate even more noise, but they are usually not adjacent to or in bedrooms. I suspect, though, that magnetic levitation bearings make ceiling fans much less noisy. Is this the case?

Kris De Decker


@ Ville (#10)

Indeed, the fans in the tests (which are also pictured in the article above) are the newest generation of fans with higher efficiency and lower noise generation than the average fan of yesteryear. None of the subjects in the tests said that the noise bothered them. However, people were doing office work, they were not sleeping or trying to sleep. So an answer to your question would require new research.

@ Andre L (#9)

1) Your point is only valid for men, not for women, and to your information women are also to be found in offices in the western developed world. The fact that men in offices wear inappropriate summer clothing (and usually are in charge) explains in large part the phenomenon of overcooling.

The main victims of overcooling in offices are women, because they usually wear appropriate clothes in summer -- open shoes and clothes that expose more skin to the environment than just the hands and the face. If men want to keep their inappropriate costumes, let them use a fan. Japan has successfully lowered AC energy use in offices by promoting more appropriate summer clothing.

By the way, fans bring large energy savings even in combination with the typical business suit of 1 clo insulation.

2) Could you clarify this point?

3) Could you tell me where in the study you found a reference to "light sweating"? The skin also evaporates liquid when we are not sweating.

4) Now you are suddenly concerned about women! See 3

5) Since computers and other office equipment are usually tossed away after three years or so, most devices will work just fine during the operational life, even at 80% humidity. And the thought that people should subordinate themselves to AC for the benefit of office tools, strikes me as far-fetched. Maybe we could try to adapt the machines instead?

6) The study describes how in all experiments perceived air quality greatly increased with the use of fans compared to AC. So the situation would actually improve. By the way, if you read the study, you must have noticed that it includes several experiments in real office buildings, not just in climate chambers.



OTOH, there's evidence that people get less productive above 25 or 26 C.

I don't know if good fans change that much. I note "lazy heat" and "lazy tropicals" are common tropes, possibly for reason.

Kris De Decker


@ drs

That's true. In the Berkeley study, the researchers note this as one of the topics for further research. They expect fans to have a positive influence on productivity, just like AC, but this has not been studied yet.

On a side note, us being so productive is probably one the main causes of resource depletion and other evils. I live in a country where people still have a siesta in afternoon during summer. Not very productive I guess, but we have the highest life expectancy and one of the happiest populations in Europe. And almost no AC.



This is good idea: https://www.youtube.com/watch?v=6ScZiMiva9M
He lets moisture into house at the lower level, moisture evaporates and absorbs heat, at the higher level is extractor which throws out humid air. claims low energy expense. The system could be improved to make more natural flow of moisture and air, hopefully eliminating the need for any extra energy input.



Evaporative coolers are ubiquitous in the high deserts of the Southwest US. Here in Denver I have rental properties with no A/C and @ 100F outside the inside temp never exceeds 78. I've seen different numbers, but Wikipedia pegs EC @ 1/8th the cost of compressor A/C. Plus the amount of water they use is trivial compared to other household water consumption.



Loved the article. Thanks.
Just to highlight the "Peak Power Demand" aspect of a/c, in Australia where I live it is estimated that the installation of a 2 kilowatt reverse-cycle air conditioner can cost a consumer around $1500, but imposes costs on the energy system of up to $7000 by adding to peak demand. Costs that are spread across all customers.
In other words, energy efficient households with fans are subsidizing energy-inefficient ones with a/c because the former pay the same for a kWh, but it's the latter who raise that cost ($/kWh).
"Cost reflective pricing" is the buzz term here nowadays. Make a/c users pay the real cost they impose on the energy system and fans (+ building standards) will have their day again. Real revenge.



Right on Kris.

I absolutely f**cking hate air conditioning.

Fair enough it has its uses in very hot countries as you have pointed out, but for example here in the UK we have it in our office, it is probably on about 6 months per year and centrally controlled so there is no getting away from it. I go to work in shorts and T-Shirt and then have to put a jumper on in the office... I mean... WTF!!!!???!! And this is at a company that champions its own "green agenda". Idiotic to the max.

Apologies for the strong words but I would be happy to see the back of AC altogether, in the UK at least!

I don't think I've posted a comment before but have to say I love your site, it has taught me so much and each article is very well researched and presented (Still got loads of back articles to read though!). Kudos to you sir.



I've been in movie theaters where I was too cold with t-shirt and long jeans. The theatre had their AC on max. I do not agree to banish AC altogether, just turn the central thermostat up a few degrees. I like the idea in a hot and dry climate to use AC to supplement a swamp cooler, and fans.

I try to maintain a balance with the outside world. I do not desire to take heaters and AC for granted, and I do want AC during the hottest days of the year and heat during the coldest nights of the year. What I am saying is, I consider my external temperature range to be around the 65 to 75 degree range in Fahrenheit.



This is all very well, but there are plenty of people who cannot tolerate ceiling fans at all. The beating motion of the blades is a migraine and seizure trigger, particularly bad when there's lighting behind the fan or even just nearby. I have to turn right around and immediately leave any room that has a ceiling fan running. If I don't get out quickly enough, I'm saddled with a migraine that lasts at least into the next day. I don't love A/C, but I'm not alone in my inability to tolerate ceiling fans.

Sherwood Botsford


Peak demand can be reduced by adding a level of indirection: Cool water and store it for later use. This allows a cooling unit to be sized to the overall demand for the day, instead of being sized for the peak demand -- a size reduction of about 60%. If the price differential between peak and non-peak time is sufficient, then sizing your unit to chill water during the lowest rate period makes sense.



You say "(circulating fan)can only provide cooling at air temperatures below the mean skin temperature, which is about 35°C"

Are you sure about that? Circulating fan stimulate sweat evaporation. This work at any temperature.
I mean... if the suronding air could not cool our body down, then human would die within minutes if temperature get above 35°C. Of course we don't rely on cool air to cool down our body!

The 35°C treshold might be true for 100% relative humidity



I'm curious how underground rooms can fit into a house's cooling system. Our house is built on a hill, and the storage room is dug into the hill, so it the summer it is a couple degrees cooler than the rest of the house. If you had a fan/air circulation system that took advantage of underground rooms, I imagine you could somewhat simulate AC but with natural cooling.

Also, I wouldn't write off glass completely. It helps light buildings naturally, and as glass insulation improves, it is less of a problem equalizing the indoor temp with the outdoor one, though it does still let the solar heat come through.



Much of this seems to ignore the fact that one of the biggest drivers of AC use, in certain environments, is in fact for humidity control more than temperature control. The textile industry, for example, was an early adopter to help control fabric properties during processing. In such cases I'm not certain there is any good replacement.

Additionally, you do your own arguments a disservice when you make seemingly petulant comments such as calling men's clothing "costumes" and implying that posters such as Andre are somehow sexist. You should really leave such personal prejudices at the door if you want to be taken more seriously...

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